Cable looping means



April 8, 1969 w. C. HART CABLE LOOPING MEANS Sheet Original Filed Jan.22, 1964 W. c. HART CABLEILOOPING MEANS April 8, 1969 Sheet ofS OriginalFiled Jan. 22, 1964 I NVENT OR Why/v5 fl/Yfler ATTORNEYS April 8, 1969wfc. HART 3,437,316

CABLE LOOPING MEANS Original Filed 31 11322, 1964 Sheet 3 of 5 BY 4, dZiw a? ATTORNEYS A rils, 1969 w. c. HART 3,437,316

CABLEILOOPING MEANS Original Filed Jan. 22, 1954 Sheet 4 of 5" k I I .3).a 7% 76 3 W Warn/E [3 192727- I ATTORNEYS April 8, 1969 wfc. HART CABLELOOPING MEANS Sheet Original Filed Jan. 22. 1964 INVENTOR WflX/VE EUnited States Patent U.S. Cl. 254-190 2 Claims ABSTRACT OF THEDISCLOSURE The invention relates to a tubular cable looping means havingthe general form of a closed loop for providing a longitudinallyextending passage in a plank to be prestressed with two lengths ofcable.

This is a division of applications Ser. No. 339,506, filed Jan. 22,1964, now Patent No. 3,283,457 and Ser. No. 567,026 filed June 2, 1966,now Patent No. 3,341,176.

The present invention relates generally to prestressed concrete and,more particularly to a new and improved method and apparatus for formingprestressed concrete slabs or planks, as well as a new and improvedprestressed concrete plank construction.

There is disclosed in the patent to Vander Heyden, No. 2,696,729, amethod of forming concrete slabs wherein reinforcing rods are carried inaligned, opposed channels or passages in a plurality of concrete blocks.The blocks are placed under temporary compression by tensioning aclamping rod extending through aligned openings in the plurality ofblocks and the channels containing the reinforcing rods are filled withgrout along this stressed row of blocks, and the grout is allowed to setwhile the clamping rod is maintained under temporary tension. After thegrout has set so as to bond the reinforcing rods to the blocks, thetension on the clamping rod is released and the clamping rod removed tothereby transfer the tension to the bonded reinforcing rods and completethe reinforced slab construction.

Likewise, means for introducing grout under pressure in these opposedlongitudinal channels or passages from the ends of the row are taught inthe patent to Carper, No. 2,897,570. While such prior art method andmeans for forming concrete slabs have enjoyed varying degrees ofsuccess, such a teaching necessarily is tedious, expensive and timeconsuming, requiring excessive clamping rod handling and storagefacilities.

Remembering that the degree or portion of the initial prestress of aconcrete plank is lost due to plastic flow, creep stress and the like,the above described prior art provisions for forming a prestressed plankof performed concrete blocks necessarily provide only a nominal degreeof prestressing. When the only stress placed on the plank is by thetension elements, which is retained after the initial compression of theplank is relieved, the resulting degree of prestress is inherentlyrelatively small.

In addition, because of the relatively low tensile strength of the mildsteel bar or rod stock employed as reinforcing elements in the priorart, it was frequently necessary to employ numerous relativelyexpensive, relatively large diameter rods in order to obtain the desiredamount or degree of prestress in the finished concrete plank. Moreover,the time consuming arrangement of such relatively expensive rods withinthe plank further increased the costs of manufacture.

Additionally, prior reinforced concrete plank constructions frequentlyhave resulted in undesirable stress pat- 'ice resulting in additionaltime-consuming assembly requirements.

According to this invention, the shortcomings of the prior art areobviated by initially compressively stressing a preformed row ofconcrete blocks by imparting tension to one or more lengths of cablepassed through the row of blocks. As will be more fully describedhereinafter, the reaction force resulting from such tensioning of thecable Will place the plank formed from these aligned blocks under thedesired compressive stress. By virtue of this, a notably superiorprestressed concrete plank is provided which does not rely on relaxing acompressed row of blocks as the sole means for imparting a prestress tothe plank via tension rods.

This invention generally contemplates prestressed concrete planks formedfrom a plurality of specially constructed concrete blocks, each havingcentrally located apertures or holes which, when aligned, define alongitudinally extending cable receiving passage wherein one or morelengths of cable are passed through the passage from end to end of theblock row and then tensioned so as to place the row of blocks undercompression. Preferably, each of the concrete blocks is additionallyprovided with laterally spaced opposed holes which, when the blocks arealigned, define laterally spaced longitudinally extending opposedpassages wherein reinforcing members such as steel rods are disposed.Thereafter the cable containing passage and the reinforcing membercontaining passages are filled with grout which is allowed to set Whilethe cable is maintained under tension. Most desirably, certain spacedapart blocks along the row have transverse, passages communicating withthe longitudinal passages so as to receive grout under pressure alongthe length of the block row, from a suitable apparatus. To this end, anovel cable guide and tensioning arrangement are provided to temporarilystress the cable.

Accordingly, a principal object of the present invention is to provide anew and improved prestressed concrete plank construction.

An additional object of the present invention is to provide a new andimproved method of making a prestressed concrete plank embodying mynovel construction.

A further object of the present invention is to provide a new andimproved apparatus for making a prestressed concrete plank embodying mynovel construction.

A further object of the present invention is to provide an improvedprestressed concrete plank construction having the desired degree ofprestress without the necessity of employing relatively expensive andnumerous relatively large diameter reinforcing rods.

A still further object of the present invention is to provide a new andimproved method of making a prestressed concrete plank from a pluralityof aligned concrete blocks which is relatively inexpensive andeliminates the need for employing separate clamping rods or the like toapply temporary initial compressive stress to the aligned blocks.

An additional object of the present invention is to provide a new andimproved prestressed concrete plank construction comprising a pluralityof aligned preformed concrete blocks having a transversely centeredlongitudinally extending passage wherein prestressed cable portions arepositioned within the passage so as to provide the plank with enhancedload carrying capabilities.

Another object of the present invention is to provide a new and improvedprestressed concrete plank construction comprising a plurality ofaligned preformed concrete blocks having a transversely centeredlongitudinally extending passage wherein a prestressed cable ispositioned within the passage in a generally parabolic or arcuate curveto provide the plank with enhanced load carrying capabilities.

A further object of the present invention is to provide a novel methodof making a new and improved prestressed concrete plank constructioncomprising a plurality of aligned preformed concrete blocks having atransversely centered longitudinally extending passage wherein aprestressed cable is positioned within the passage in a generallyparabolic or arcuate curve to provide the plank with enhanced loadcarrying capabilities.

Another object of the present invention is to provide a new and improvedprestressed concrete plank construction which eliminates splitting orcracking of the plank resulting from undesirable stress concentrations.

A still further object of the present invention is to provide a new andimproved concrete plank construction formed of individual preformedconcrete blocks having a longitudinally extending passage carrying atensioned cable and including means at each end of the plank to preventthe longitudinal cracking occasioned by localized compressive stress onthe plank due to the tensioned cable.

Other objects and advantages of the invention will become apparent fromthe following description and accompanying drawings in which:

FIGURE 1 is a perspective view showing the prestressing of a concreteplank according to this invention;

FIGURE 2 is a sectional view taken along the line 22 of FIGURE 1;

FIGURE 3 is a perspective view of a concrete block employed in forming aprestressed concrete plank according to the present invention;

FIGURE 4 is a perspective view of a tie plate which is employed in theprestressed concrete plank shown in FIGURE 1;

FIGURE 5 is a plan view, partly in section, of the rear cable guideassembly employed in the prestressing of the concrete plank shown inFIGURE 1;

FIGURE 6 is a side view, partly in section, of the rear cable guideassembly shown in FIGURE 5;

FIGURE 7 is an enlarged perspective view of the front cable guideassembly and tensioning means employed in the prestressing of theconcrete plank shown in FIGURE FIGURE 8 is a longitudinal sectional viewof the concrete plank shown in FIGURE 1 prior to prestressing;

FIGURE 9 is a longitudinal sectional view of the concrete plank shown inFIGURE 1 after prestressing and grouting;

FIGURE 10 is a longitudinal sectional view of the prestressed concreteplank shown in FIGURE 9 after the grout has set and the front and rearcable guide assemblies have been removed;

FIGURE 11 is a longitudinal sectional view showing a modified form ofthe present invention;

FIGURE 12 is a side view showing another modified form of the presentinvention;

FIGURE 13 is a perspective view, partly in section, illustrating stillanother modified form of the present 1nvention;

FIGURE 14 is a side view showing a further modified form of the presentinvention;

FIGURE 15 is a perspective view, partly in section, showing anothermodified form of the present invention;

FIGURE 16 is a plan view showing a still further modified form of thepresent invention;

FIGURE 17 is an end view of another modified form of the presentinvention;

FIGURE 18 is a plan view, partly in section, of a modified rear cableguide assembly employed in forming a prestressed concrete plankaccording to the present invention;

FIGURE 19 is a side view, partly in section, of the modification shownin FIGURE 18;

FIGURE 20 is an end view showing a modified means for anchoring theclosed end of the cable during tensioning when the modificationillustrated in FIGURES 18 and 19 is employed; and

FIGURE 21 is a plan view of the modification shown in FIGURE 20.

Referring now to FIGURE 1 of the drawings there is shown a stationaryconveyor assembly 10 including a plurality of transversely extending,longitudinally spaced apart rotatably mounted rollers 12. A plurality ofsubstantially identical preformed concrete blocks 14 are arranged withtheir end faces 16 abutting and in aligned relationship on the rollers12 according to the length of the slab or plank 18 to be formed.

As best seen in FIGURES 2 and 3, each block 14, which is made ofsuitable cementitious material, is generally rectangular in shape andincludes substantially fiat and parallel upper and lower faces 20 and22, respectively, substantially parallel end faces 16 and side faces 24and 26 provided with suitable tongue and groove formations 28 and 30,respectively. Preferably, each block 14 is provided with twotransversely spaced enlarged passages 32 extending through the blockfrom one side face 16 to the other and separated by a transverselycentered vertically extending web portion 34. The enlarged passages 32not only reduce the weight of the finished plank, but also definelongitudinally extending passages for receiving electric conduits,heating ducts and the like having obvious utility where the formedplanks are to be used in floor construction. In addition, each block 14will be seen to be provided, adjacent the lower face thereof, with atransversely centered aperture 36 and laterally located apertures 38 and40 spaced transversely on either side of the central aperture 36. Eachof the apertures 36, 38 and 40 extends through the block 14 from oneside face to the other and is adapted to register with a correspondingaperture in adjacent blocks when arranged in plank forming alignment soas to define generally parallel, longitudinally extending passages.Preferably, the central aperture 36 is of a generally triangularconfiguration in cross section while the laterally located apertures 38and 40 are of a substantially circular configuration in cross section,as best seen in FIGURES 2 and 3.

Certain spaced apart blocks 14' (FIGURES 1 and 2) have vertical passages42, 46 and 48 extending from the upper face 20 of the block 14' andcommunicating with the apertures 36, 38 and 40, respectively, forreasons to be more fully described hereinafter.

If desired, tie plates 50 can be interposed between each endmost pair ofblocks 14 in order to provide the finished plank with enhancedresistance to longitudinal cracking. The tie plates 50, which arepreferably of sheet metal construction, have a pair of enlarged openings32 and smaller openings 36', 38' and 40' corresponding to, and adaptedto register with, the enlarged passages 32 and apertures 36, 38 and 40,respectively, in the adjacent blocks 14. The tie plates 50 may also beprovided with raised boss portions 52 surrounding the openings 36', 38and 40'.

After the blocks 14 are arranged in plank forming alignment, as shown inFIGURE 1, a rod member 54, having a length substantially correspondingto the length of the plank 18 to be formed, is positioned in each of thepassages defined by the aligned laterally located apertures 38 and 40.Each rod member 54, which is preferably a steel reinforcing rod, is of adiameter substantially less than the diameter of the passage in which itis received in order to provide a grout receiving space.

As best seen in FIGURES 1, 5 and 6, a rear cable guide assembly 56 ispositioned adjacent the outwardly facing end face 16 of the rear endmostblock 14 at one end of the row of blocks. The rear cable guide assembly56 generally includes a rear channel-shaped abutment member 58 having asubstantially fiat web portion 60 connecting the spaced flanges 62. Theflat Web portion 60 is provided with an aperture 64 adapted to registerwith the central aperture 36 in the rear endmost block 14 when themember 58 operatively abuts the outwardly facing end face 16 of theblock. A tubular cable looping member 66, having the general form of aclosed loop when viewed in plan, is mounted on the outwardly facingsurface of the web portion 60 in alignment with the aperture 64 so as tobe in operative cable receiving communication with the passage definedby the central apertures 36 in the blocks 14. The tubular cable loopingmember 66 includes a substantially straight, common tubular portion 68extending perpendicularly outward of the web portion 60 and having alaterally disposed cable access aperture 69' and a tubular loop portion70. The tubular loop portion 70, as best seen in FIGURE 5, includes twotubular branch portions 72 in communication with the bore of tubularportion 68 which, as they extend outwardly thereof, initially divergeand then arcuately converge to meet at their outermost extent andthereby form a closed tubular loop. The tubular cable looping member 66will thus be seen to define a closed loop-like tubular passage incommunication with the passage defined by the central apertures 36 inthe blocks 14. Preferably, the cable loop ing member 66 is provided withstrut members 74 and 75 to provide enhanced structural support, as willbe readily appreciated.

If desired, the web portion 60 of the channel-shaped abutment member58may be provided with two additional apertures (not shown) transverselyspaced so as to register with the laterally located apertures 38 and 40in the block 14 to thereby permit introduction of the rod members 54after operatively positioning cable guide assembly 56.

A front cable guide assembly 76 is positioned adjacent to outwardlyfacing end face 16 of the foremost block 14 of the row, preferablyadjacent an end of the conveyor 10, as best illustrated in FIGURES 1 and7. The front cable guide assembly 76 includes a channel-shaped frontabutment member 78 having a substantially flat web portion 80 connectingthe spaced flanges 82. The flat web portion 80 is provided with closelyspaced apertures 84 and 86 adapted to register with the adjacent centralaperture 36 in the foremost block 14 when the member 78 operativelyabuts the outwardly facing end face 16 of the block. Alternatively,instead of the two spaced apertures 84 and 86, a single, somewhat largeraperture (not shown), adapted to register with the central aperture 36,may be provided in the web portion 80. A pair of transversely spacedvertically extending plates '88 and 90 abut the outwardly facing edgesof the flanges 82 of the channel-shaped member 78. Preferably, theplates 88 and 90 are joined to the channel-shaped member 78 by weldingor the like. Also abutting the outwardly facing edges of the flanges 82of the channel-shaped member 78, intermediate the ends thereof, is avertically extending plate member 92 having apertures (not shown)axially aligned with the apertures 84 and S6 in the web portion 80.Preferably the plate 92 is. joined to the channel-shaped member bywelding or the like. The plate 92 is preferably reinforced by ahorizontally extending plate 94, as best seen in FIGURE 7.

With the front cable guide assembly 76, the blocks 14, the tie plates50, and the rear cable guide assembly 56 positioned as shown anddescribed, the leading end 96 of a cable 98, preferably steel, is passedthrough one of the apertures in the plate member 92 and thecorresponding aligned aperture, such as 84, in the front abutment member78, through the longitudinal passage defined by the central apertures 36in the blocks 14, through the aperture 64 in the rear abutment member 38and into the common tubular portion 68 of the tubular cable loopingmember 66. Continued longitudinal feeding of the cable 98 will cause theleading end 96 to pass into one of the tubular branch portions 72 whereit will be guided in a generally U-shaped path to form a loop and enterthe other tubular branch portion 72 and thence return through the commontubular portion 68, the aperture 64, and the passage defined by thecentral apertures 36 in the blocks 14 until the leading end 96 emergesfrom the other aperture 86 in the front abutment member 78 so that theopposed leading end 96 and trailing end 100 extend through and outwardlybeyond the vertically extending plate 92 of the front cable guideassembly 76. Thus it will be seen that two lengths of cable will bedisposed in the passage defined by the central apertures 36 in theblocks 14.

As best seen in FIGURES 1 and 7, there is provided a means 102 fortensioning the cable 98 by pulling the cable ends 96 and 100. To thisend, a plate 104 has at tached to its upper surface intermediate itsends, cylindrical, internally threaded sleeves 106 and 108, the sleevesbeing axially aligned with the apertures 84 and 86, re

spectively, in the front abutment member 78 so that the cable ends 100and 96 may be operatively received so as to extend through the sleeves106 and 108, respectively. Threadedly received in the respective sleeves106 and 108 adjacent the vertical plate member 92, are externallythreaded collars 110 and 112, having knurled heads 114 and 116,respectively, and longitudinal bores or passages adapted to freelyreceive the respective cable ends 96 and 100.

Next, vice members or cable clamps 118 and 120 are slid over therespective ends 100 and 96 of the cable 98, these clamps 118 and 120being in abutting relationship with the outer ends of the respectivesleeves 106 and 108, as best shown in FIGURE 7. The cable clamps 118 and120 are of conventional construction, and each includes a tapered outersleeve 122 and a gripping surface 124 carried by a cooperatively taperedcollar 126 of split construction.

Extending from the front end of the row of blocks defining the plank 18is a track 128, carrying a wheeled cart 130. Fixed to the cart 130 is afluid cylinder 132 having a piston rod 134 extending therefrom towardthe front end of the row of blocks. Pivotally connected to the free endof the piston rod 134, as by a removable pin 136, is a clamping assembly138 having transversely spaced perpendicularly depending end members140. By virtue of the pivotal connection of the clamping assembly 138 tothe piston rod 134, the vertically extending end members 140 mayconveniently be pivoted into and out of the space between the laterallyextending inner edge of the plate 104 and the front cable guide assembly76. The cart 130 also carries transversely spaced opposed longitudinallyextending bars or struts 142 positioned for abutment at their ends withthe outwardly facing surface of the front cable assembly 76, for reasonsto be more fully apparent hereinafter.

With the elements assembled as described, the cart 130 is moved towardthe front end of the row of blocks and the end members 140 of theclamping assembly 138 are pivoted downwardly into the space between thesleeve carrying plate 104 and the front cable guide assembly 76, asaforedescribed. The fluid cylinder 132 is then actuated to move thepiston rod 134 away from the row of blocks, so as to effect firmengagement of the end members 140 with the inner edge of the sleevecarrying plate 104 and thereafter exert tension on the cable 98 bypulling the cable ends 96 and 100 through the cooperation of the sleeves106 and 108 and the cable clamps 118 and 120, the reaction force beingtransmitted to the row of blocks through the longitudinally extendingstruts 142 carried by the wheeled cart 130. This movement of the pistonrod 134 inwardly of the fluid cylinder 132 causes the cable clamps 118and 1-20 to firmly grip the cable ends; and, when a predeterminedtension is imparted to the cable, which is preferably controlledautomatically by a pressure responsive solenoid operated valve (notshown) 7 operatively connected to the fluid source (not shown), thecollars 110 and 112 are unthreaded from their respective sleeves 118 and120 until they abut the outwardly facing surface of the vertical platemember 92. Thus, the tension imparted to the cable 98 and the consequentcompression imparted, as a reaction thereto, to the aligned row ofblocks is maintained by engagement of the collars 110 and 112 with theplate member 92. The fluid cylinder 132 is then deactuated to permitdisengagement of the end members 140 with the sleeve carrying plate 104by upward pivotal movement of the clamping assembly 138.

The row of blocks forming the plank 18, which is now subjected to thedesired predetermined degree of prestress, may be moved along therollers 12, as desired, away from the wheeled cart to permit the same tobe employed for the prestressing of another row of blocks. With the rowof blocks forming the plank 18 so stressed, grout 144 is introduced intothe longitudinally extending rod member containing passages defined bythe apertures 38 and 40 and the longitudinally extending stressed cablecontaining passage defined by the central apertures 36, through thevertical passages 42, 46 and 48 in the blocks 14 disposed along thelength of the row of blocks. By introducing the grout 144 under pressurethrough the apertures 42', 46 and 48 in the blocks 14, the longitudinalpassages are filled quite rapidly and efficiently. The grout 144 orother suitable bonding substance which is employed should be capable ofproviding a strong stress-transmitting bond between the stressed cable98 and the concrete blocks 14.

After the longitudinally extending passages defined by the apertures 36,38 and 40 have been filled with grout, the plank '18 composed of thecompressively stressed blocks 14 is permitted to set a sufiicient timeto allow the grout to set thereby fixing the cable 98 under stresswithin its longitudinally extending passage as well as operativelysecuring the rod members 54 within their respective longitudinallyextending passages. Thereafter, the front and rear cable guideassemblies 76 and '56, respectively, are removed as by burning orcutting the exposed portions of the cable 98 at the front cable guideassembly 76, between the vertical plate member 92 and the web portion 80of the channel-shaped member 76, and at the rear cable guide assembly 56through the cable access aperture 69 in the cable looping member 66. Aswill be apparent, the sleeves 106 and 108, collars 110 and 112 and cableclamps 118 and 120 may be reused after removal of the severed cable ends96 and 100 therefrom.

The tendency of the compressed concrete blocks 14, in the finishedprestressed plank 18, to expand after removal of the front and rearcable guide assemblies 76 and 56, respectively, is resisted entirely bythe grouted tensioned cable 98 without any transfer of tension to thegrouted rod members 54. Thus, the aforementioned limitations anddisadvantages inherent in the prior art wherein the initial prestressapplied during forming of a prestressed plank is transferred to bondedreinforcing rods are effectively and simply overcome. The laterallydisposed longitudinally extending grouted rod members 54 not only resistany tendency of the blocks 14 to twist relative to one another about thelongitudinally extending transversely centered axis defined by thetensioned cable 98, but also provide the formed plank 18 with enhancedload carrying capabilities, as will be more fully described hereinafter.

The tie plates 50, of course, are retained within the formed plank 18 bythe grouted and stressed cable 98 and the grouted rod members 54. Thus,it has been found that prestressed concerte planks 18 formed of blocks14 and prestressed grouted cable 98, as described, retain a notablysuperior resistance to longitudinal cracking by provision of the tieplates 50 disposed adjacent the opposed end regions of the formed plank'18 so as to distribute the local stresses throughout the crosssectional area of the plank 18.

Reference is now made to FIGURES 8 and 9 wherein there is shown therelative disposition of the cable 98 within the longitudinally extendingpassage defined by the central apertures 36 in the aligned blocks 14 andthe disposition of the block 14 before and after, respectively, theaforedescribed application of prestrcssing tension to the cable 98. InFIGURE 8, before the application of prestressing tension to the cable98, the aligned blocks 14 will be seen to be disposed in a substantiallystraight condition with the cable 98 similarly disposed along the topsurface of the longitudinally extending passage defined by the centralapertures 36 in the blocks 14. As best seen in FIGURE 9, application ofthe desired prestressing tension to the cable 98, which is disposedbelow the vertically centered longitudinal axis of the plank 18 adjacentthe lower faces 22 of the blocks 14, will result in upward verticaldisplacement of centrally located blocks relative to the end blocks,thereby causing the plank 18 to assume a slight camber or archedconfiguration and thus dispose the cable 98 at the longitudinal centralportion of the plank 18 adjacent the lower surface of the passagedefined by the central apertures 36. At each end of the plank 18, theends of the tensioned cable 98 will remain disposed adjacent the uppersurface of the passage defined by the central apertures 36 since thetensioned cable 98 remains in a substantially straight condition. Thepassage defined by the central apertures 36, which will be seen to haveassumed the form of a positive curve of arcuate or parabolicconfiguration, is then filled with grout 144, which is allowed to set,as aforementioned. Thus, the cable 98 will be fixed within the curvedpassage defined by the central apertures 36 so that the end portionsthereof are adjacent the upper surface of the passage at the ends of theplank, while the central portions of the cable 98 are adjacent the lowercentral surface of the passage.

After the grout has set and the front and rear cable guide assemblies 76and 56, respectively, have been removed, the plank 18 will be in theaforedescribed arched condition, as best seen in FIGURE 10. Due to thefact that the cable 98 has become set within the grout 144, the centralportion of the cable 98 will be seen to be maintained adjacent thecentral lower portion of the central passage while the cut ends areadjacent the upper surface of the passage at the ends of the plank 18.

Referring now to FIGURE 11 of the drawings, there is shown a modifiedform of the present invention wherein a support member 146 having anarcuate supporting surface 148 is employed to support the prestressedand grouted plank 18 in a predetermined arched condition while the grout144 is setting. Thi modification, employing the support member 146, isparticularly useful where the amount or degree of tension applied to thecable 98 to prestress the plank 18 may not in and of itself effect thedesired amount of camber or arching of the plank 18 and thus effect theaforedescribed desired disposition of the cable 98 during the setting ofthe grout 144. The arcuate supporting surface 148 will be seen tosupport the central portion of the plank 18 at a higher elevation thanits ends so that the cable 98 at the longitudinal center of the plank 18is closely adjacent the lower surface of the passage defined by thecentral apertures 36 while the cable ends are adjacent the upper surfaceof the pas sage at each end of the plank in a fashion substantiallysimilar to the embodiment described by reference to FIG- URE 9. Afterthe grout 144 has set, the front and rear cable guide assemblies 76 and56, respectively, are removed as aforementioned, and the supportingmember 146 is removed from the underside of the plank 18. The formedprestressed plank 18 will then relax somewhat so as to assume the lessercamber or arched configuration which is imparted by the tensioned cable98 alone, substantially similar to that aforedescribed by reference to,and shown in, FIGURE 10. The tensioned cable will assume a slightlynegative or upwardly concave curve with the cut ends of the cableadjacent the upper surface of the central passage and the centralportion of the cable at the longitudinal center of the plank 18 closelyadjacent the lower surface of the passage.

While the limited controlled arching or camber of a prestressed concreteplank as aforedescribed is frequently desirable, it should also be notedthat an excessive arching or camber can impair the functioning of theprestressed plank. Such undesirable excessive arching of the plank mayoccur during formation of the plank as a result of the initialcompression of the blocks by the tensioned cable, or can occur with thepassage of.time through what is believed to be a creep phenomenon. Thelast-mentioned cause of excessive arching which may be called long-termarching or long-term camber, is believed to result from a slow butcontinuing shortening of the plank below its vertically centered,longitudinal axis due to the longitudinal compression of the plankimparted by the tensioned cable. Such long-term arching can ultimatelyimpair the function of the prestressed concrete plank to such an extentthat its removal and replacement will be necessary. In prestressedconcrete planks constructed according to the teachings of the instantinvention, such long-term arching has been effectively controlled, byvirtue of the laterally spaced rod members disposed below the verticallycentered longitudinal axis of the plank. It has been observed that ashort time after the grout has set and the plank has been completed, therod members, which are bonded to the plank by grout, are undercompression. It is believed that the rod members are thus effective tocontrol and limit such long-term arching by resisting the tendency ofthe plank to shorten below its vertically centered longitudinal axis.Thus, it will be apparent that an effective, simple and inexpensivemeans of controlling long-term arching or long-term camber has beenprovided by employing the rod members 54, as aforedescribed.

Reference is now made to FIGURE 12 of the drawings wherein there isshown a modified form of preformed concrete block 114 which can beemployed in the present invention to form a prestressed plank 118. Theblock 114 differs from the block .14, just described, in that the upperface 120 is slightly shorter than the lower face 122 so that the endfaces 116 are not parallel but taper or upwardly converge as shown,greatly exaggerated, in FIGURE 12. As was the case with the blocks 14,the blocks 114 are provided adjacent the lower face 122 thereof, with atransversely centered aperture 136 and laterally locate-d apertures 140spaced transversely on either side of the central aperture 136, whichare adapted to align with corresponding apertures in adjacent block-s soas to define longitudinally extending passages. When the blocks arearranged in plank forming alignment, a small upwardly openingwedge-shaped space 150 will be formed between the opposed end faces 116of adjacent blocks 114. The use of blocks 114 having upwardly convergingend faces 116 to form a prestressed plank 1518, as aforedescribed, willlimit the amount of initial camber or arching of the plank which resultsfrom the tensioning of the cable and consequent compression of thealigned blocks. Thus, this modification utilizing blocks 114 havingupwardly converging end faces 116 is particularly useful whereprestressing would normally result in an excessive or undesired amountof camber or arching of the plank.

Reference is now made to FIGURE 13 of the drawings which illustratesanother modified form of the present invention wherein a plurality oflongitudinally aligned prestressed concrete planks 218, 218 and 218" aresimul- 'taneously formed. The embodiment of the invention shown inFIGURE 13 differs from that aforedescribed by particular reference toFIGURES 1 7, in that spacer members 202 are interposed between adjacentconcrete blocks 214 at preselected positions along the row. Thus thedisposition of the spacer members 202 relative to the front and rearcable guide assemblies 276 and 256, respectively, will determine thelengths of the planks 218,

218' and 218". The spacer member 202 are preferably metal plates bent orotherwise formed into the shape of a rectangle having longitudinallyspaced vertical end walls 204 adapted to engage the opposed end faces216 of adjacent blocks 214. Each vertical end wall 204 of the spacermembers 202 is provided with a transversely centered aperture 206 andtwo laterally located apertures 208 spaced transversely on either sideof the central aperture 206. The central aperture 206 and laterallylocated apertures 208are adapted to align with the correspondingapertures 236, 238 and 240, respectively, in the ad jacent blocks 14when the spacer members 202 are operatively disposed along the row ofaligned blocks.

Certain spaced apart blocks 214 have vertical passages 242, 246 and 248communicating with the apertures 236, 238 and 240, respectively, tofacilitate the introduction of grout under pressure in the planks 218,218' and 218'. In addition, tie plates 250, substantially identical tothe aforedescribed tie plates 50, can be interposed between each endmostpair of blocks 214 in each of the planks 218, 218 and 218".

The plurality of prestressed planks 218, 218' and 218" are formed simplyin a manner substantially similar to that described by reference toFIGURES 1-7. Thus, after the rod members 254 are positioned in thelongitudinally extending lateral passages defined by the laterallylocated apertures 238 and 240 in the blocks 214, a cable 298 is passedthrough the aligned central aperture 236 of the entire row of blocks214, which is segmented into planks 218, 218' and 218" by the spacermembers 202. As aforedescribed, the looping member 266 of the rear cableguide assembly 256 will guide the leading end 296 of the cable 298 in agenerally U-shaped path to form a loop whereby continued feeding of thecable 298 will return the leading end 296 through the cable receivingpassage defined by the apertures 236 so that two lengths of cable willbe disposed in each plank 218, 2.18 and 218". Thereafter, prestressingtension is applied to the cable 298 to thereby place the blocks 214forming the planks 218, 218 and 218" under prestressing compression andthe cable 298 and rods 254 are then groute-d in place, all in a mannersubstantially identical to that aforedescribed by reference to FIGURES1-7.

After the grout has set, the row is broken into its individual planks218, 218 and 218" by burning or otherwise cutting the cable at its endsto remove the rear and front cable guide assemblies 256 and 276,respectively, as well as severing the exposed cable 248 and rod members254 which are visibly accessible from the open sides of the spacermembers 202. Thus, when the block row in FIGURE 13 is broken down, threeslabs 218, 218' and 218" are formed by a single stressing operation onthe whole row. As will be appreciated, the length of the rows and thenumber of slabs formed is readily adjusted by the particular demand, andspecial equipment or the like is not required to change the slab lengthsas well as the number of slabs formed by a single cable stressing step,as previously described.

Turning now to FIGURE 14, there is shown a modified arrangement forobviating the transmission of undesirable stress along the end regionsof the prestressed plank which cause a longitudinal cracking of theplank along the cen tral vertical plane thereof due to the greaterstress at the greater stress at the ends, which longitudinally compressthe concrete at these localized end regions. There is shown here an endblock 314 of the plank 318, having bevelled upper and lower cut-outportions 300 and 302, respectively, adjacent its inner end face 316.Transversely extending reinforcing rods 304 and 306 are positionedwithin these bevelled portions 300 and 302 respectively, and securedwith grout 344. As the plank 318 is not subjected to these localizedcompression stresses during the grout setting stage due to thechannel-shaped members of the front and rear cable guide assemblies, thegrout'can set while the grout introduced into the longitudinallyextending passages is also setting. When the setting has been completedand the cable guide assemblies are removed, the undesirable local stressin the plank 318 is eflficiently distributed throughout the surfacethereof via the reinforcing rods 304 and 306 and their surrounding grout344. Thus, the reinforcing rods 304 and 306 and grout perform anequivalent function to that of the tie plates 50. Accordingly, themodification is equally applicable to the various other modificationsdescribed herein, as the end blocks in each prestressed plank may be soformed.

In FIGURE 15, still another modification of the plank construction isprovided, wherein the outside end face 416 of the endmost blocks 414have upper and lower transverse recesses 400 and 402 inwardly of thecorners thereof, which carry reinforcing rods 404 and 406, respectively,in grout. By virtue of this arrangement, the tendency of the endmostblocks of the planks to crack longitudinally, as aforedescribed, isobviated. The end blocks 414 may be conveniently formed prior toassembly of the plank or simultaneously with the formation thereof, asdesired.

Also, depending on the degree of stress in the cable lengths, the blockwidth configuration and so forth, the end blocks 314 (FIGURE 14) or 414(FIGURE 15) may be formed with reinforcing at one end edge only, as

necessary.

Referring now to FIGURE 16 of the drawings, there is shown anothermodified form of prestressed concrete plank 518 embodying the invention.The construction of the prestressed concrete plank 518 differs from thatof the prestressed concrete plank 18, aforedescribed, in that thelongitudinally extending passage defined by the transversely centeredapertures 536 is provided with only a single length of tensioned cable598. Since only one length of cable 598 is disposed within thelongitudinal passage defined by the central apertures 536, it is notnecessary to employ my novel cable looping member 66, aforedescribed.Thus, the cable 598 can be anchored at the rear end of the plank 518 bymeans of a conventional cable clamp 500 embodying substantially the sameconstruction as the cable clamps 118 and 120, aforedescribed. To thisend, a modified rear cable guide assembly 556, similar to theaforedescribed front cable guide assembly 76, is provided. The rearcable guide assembly 556 includes a rear channel-shaped abutment member558 having a substantially flat web portion 560 connecting a pair ofspaced flanges 562. The flat web portion 560 is provided with anaperture 564 adapted to register with the central cable containingaperture 536 in the rear endmost block 514 when the abutment member 558operatively abuts the outwardly facing end face 516 thereof. Abuttingthe outwardly facing edges of the flanges 562 of the channel-shapedabutment member 558 is a vertically extending plate member 566 having anaperture 568 axially aligned with the aperture 564 in the web portion560 of the abutment member. The front cable guide assembly 576 is of aconstruction substantially identical to that of the aforedescribed frontcable guide assembly 76, and includes an apertured channel-shapedabutment member 578, a pair of transversely spaced vertically extendingplates 588 and a transversely centered, operatively aligned aperturedplate 592 abutting the channel-shaped abutment member. The means fortensioning the cable is substantially similar to the means 102,aforedescribed, and includes an internally threaded sleeve 506, anexternally threaded collar 510 having a knurled head 512 and a cableclamp 520.

Prestressing of the plank 518 formed by the aligned row of blocks 514 isaccomplished in a manner substantially similar to that aforedescribed byreference to FIG- URES 1-7, with the exception that only a single lengthof cable 598 is disposed within the blocks. Thus, after the rod members554 are positioned in the longitudinally extending lateral passagesdefined by the laterally located apertures 538 and 540 in the blocks514, and the front and rear cable guide assemblies 57 6 and 556,respectively, are

operatively positioned at the ends of the plank 518, a single length ofcable 598 is positioned within the longitudinally extending passagedefined by the centrally located apertures 536 in the aligned blocks 514with the opposed ends thereof, 594 and 596, extending outwardly beyondthe vertically extending plates 592 and 566. With the cable clamp 500operatively engaging the cable end 596 and the sleeve 506, collar 510and clamp 520 operatively positioned on the other cable end 594, theplank 518 is subjected to the desired degree of prestress by tensioningthe cable 598, as in the embodiment of the invention described byreference to FIGURES 1-7. The collar 510 is then unthreaded so as toabut the vertical plate member 592 and thereby maintain the cable 598under the desired prestressing tension and the blocks 514 undercompression during introduction and setting of the grout in thelongitudinally extending rod and cable containing passages. As in theaforementioned embodiments, the front and rear cable guide assemblies576 and 556, respectively, are removed by severing the exposed endportions of the cable 598.

Reference is now made to FIGURE 17 of the drawings wherein there isshown a further modified form of a preformed concrete block 614 whichcan be employed to form a prestressed concrete plank according to theinvention. The block 614 differs from the block 14, aforedescribed, inthat the transversely centered aperture 636 adapted to receive theprestressing cable 698 has a vertically elongated generally rectangularconfiguration in cross section, the upper and lower edges 632 thereofpreferably being curved or arcuate. This modified block construction 614has particular utility where only a single length of cable 698 isdisposed within the prestressed plank, as just described by reference toFIGURE 16.

Reference is now made to FIGURES 18, 19, 20 and 21 of the drawings,wherein there is shown a modified rear cable guide assembly 756 and amodified arrangement for anchoring or restraining the closed or loopedend of the cable 798 during formation of the prestressed plank 718. Therear cable guide assembly 756 differs from the rear cable guide assembly56, aforedescribed, in that the tubular cable looping member 766 isadapted to be removed after forming the cable 798 into a loop and priorto tensioning of the cable. To this end, the tubular cable loopingmember 766 is of a separable or split construction and includes top andbottom sections 770 and 772 having mating flanges 774 and 776,respectively. The top and bottom sections 770 and 772 are held togetherin operative association by suitable removable fastener means such asbolts 778 which extend through the opposed mating flanges 774 and 776.The common tubular portion 768 is preferably provided with flanges 780,through which suitable fastener means, such as bolts 782, extend so asto removably secure the tubular cable loopin member 766 to the web 760of the rear channel-shaped abutment member 758. When assembled andoperatively positioned adjacent the rear channel-shaped abutment member758, the tubular cable looping member 766 will be seen to define aclosed loop-like tubular passage in communication with the central cablereceiving passage in the plank 718. After the cable 798 has beendisposed within the central cable receiving passage in the plank 718 bybeing guided through the tubular cable looping member 766 in a generallyU- shaped path to form a loop, in a manner substantially similar to thatdescribed by reference to FIGURES 1-7, the bolts 778 and 780 are removedto thereby permit disassembly and removal of the tubular cable loopingmember 766.

As best seen in FIGURES 20 and 21, after the tubular cable loopingmember 766 has been removed from operative association with the closedor looped end of the cable 798 and the rear channel-shaped abutmentmember 758, a bar member 784 is disposed within the now exposed, closedor looped end of the cable 798. Upon the application of prestressingtension to the cable 798, as aforedescribed, the bar 7 84 will engageboth the rear channelshaped abutment member 758 and the closed end ofthe cable 798 so as to anchor or restrain the closed end of the cable tothereby permit tCI'lSl OI'lllIlg of the same during the groutingoperation. After the grout has set, the exposed, closed end of the cable798 is severed, as by buming or cutting, so as to permit removal of thebar member 784 and the rear channel-shaped abutment member 758 fromoperative association with the plank 718.

It will thus be seen that the objects of this invention have been fullyand effectively accomplished. It will be realized, however, that theforegoing specific embodiments have been shown and described only forthe purpose of illustrating the principles of this invention and aresubject to extensive change without departure from such principles.Therefore, this invention includes all modifications encompassed withinthe spirit and scope of the following claims.

What is claimed is:

1. A cable looping means for providing a longitudinally extendingpassage in a plank to be prestressed with two lengths of cablecomprising: an arcuate cable guiding surface adapted to operativelycommunicate with one end ofsaid passage so as to receive the leading endof a cable passed through said passage by longitudinally feeding thecable from the other end thereof and guide said leading end in anarcuate path to thereby form the cable into a loop and return saidleading end to said passage so that continued feeding of the cablelongitudinally of said passage will return said leading end to the saidother end of said passage whereby two lengths of cable will be disposedwithin said passage.

2. The apparatus defined in claim 1 wherein said cable looping meansincludes a first tubular portion, the bore of said first tubular portionat one end being adapted to operatively communicate with the passage anda second tubular portion defining an arcuate cable guiding surfacecommunicating with the bore of said first tubular portion at the otherend thereof.

References Cited UNITED STATES PATENTS

